Add ScatterOp no-op simplification patterns#2920
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brucechanglongxu wants to merge 1 commit intoopenxla:mainfrom
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Add ScatterOp no-op simplification patterns#2920brucechanglongxu wants to merge 1 commit intoopenxla:mainfrom
brucechanglongxu wants to merge 1 commit intoopenxla:mainfrom
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Two new patterns in StablehloAggressiveSimplification: - ScatterOpEmptyIndices: when scatter_indices has zero scatter points along any non-index_vector_dim axis, the scatter is a no-op and the inputs pass through unchanged. - ScatterOpZeroExtentUpdates: when all update tensors have zero elements, the scatter does nothing. Both follow the existing convention for no-op detection (cf. DynamicUpdateSliceOp_RemoveNoop, ConcatenateOpRemoveEmpty). Toward openxla#2736
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ScatterOp had zero simplification patterns — even trivially dead
scatters were being left in the IR. This adds two no-op patterns to
StablehloAggressiveSimplification:
ScatterOpEmptyIndices — scatter_indices has no scatter points (a
non-index_vector_dim axis is 0), so nothing gets scattered. The
inputs pass through.
ScatterOpZeroExtentUpdates — all update tensors have zero elements,
same result.
These mirror the existing DynamicUpdateSliceOp_RemoveNoop /
ConcatenateOpRemoveEmpty patterns. More interesting patterns (e.g.
full-replace folding when the update body is a trivial return of arg1)
can come later, but these two cover the low-hanging fruit.
Tests included for both patterns plus a negative case to make sure we
don't over-simplify.
Toward #2736